Partulina semicarinata (Lanai tree snail, pupu kani oe), a member of the family Achatinellidae and the endemic Hawaiian subfamily Achatinellinae, is known only from the island of Lanai (Pilsbry and Cooke 1912–1914, p. 86). The shell may coil to the right (dextral) or left (sinistral), but appears to be constant within a population. The oblong to ovate shells of the adult are 0.6 to 0.8 in (16 to 20 mm) long, have 5 to 7 whorls, and range in color from rusty brown to white, with some individuals having bands around the shells. The shell has a distinctive keel that runs along the last whorl, and is more distinctive in juveniles. The shell may coil to the right (dextral) or the left (sinistral), and both types of shells can be found in a single population. Only snails with the same coil type can mate. Partulina tree snails reach adult size in 4 to 7 years. Upon reaching adult size, the snails stop growing and form a thickened edge or lip along the opening of the shell. A tree snail may attain an age that exceeds 15 years.